The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Water remediation is an essential part of process systems in the oil and gas industry. Process water in the oil and gas industry can contain hydrocarbon contaminants such as oil. Fluid mixtures of this type, which includes components of different densities, can be separated using gas flotation technologies, such as Dissolved Gas Flotation (DGF), Induced Gas Flotation (IGF), or combinations or variations of these. Conventional gas flotation apparatus generally need to be large vertical or horizontal vessels to provide a long fluid flow path which allows the oil and water mixture to be held within the apparatus for a defined retention time. However, space is at a premium in the oil and gas industry, particularly on offshore platforms, floating vessels, and within onshore facilities. It is therefore desirable to enhance gas flotation to recover as much residual oil as possible using other means in order to reduce the size of the vessels.
In some cases, separation can be enhanced by imparting a rotational flow to the fluid mixture within the vessel. Fluid rotation can impart a centrifugal/spiral flow pattern into the fluid mixture which increases the flow path and therefore retention time within a vessel. Furthermore, with sufficient rotation, a fluid component with a lower density migrates toward a central axis of the rotational flow and a fluid with a higher density migrates toward a periphery of the rotational flow in response to centripetal and/or centrifugal forces generated by the rotational flow. This and other separation enhancements can provide more compact separation apparatus for separating the oil from water in such wastewater.
A number of compact separation vessels are currently available.
One prior compact separator is taught in International Patent Publication WO2007/049246 A2. This separator comprises a cylindrical vertical tank having an upwardly protruding conical frusta shaped wall dividing the tank into an upper section and a lower section. The upward protruding conical frusta shaped wall has at least one opening which allows communication between the upper section and the lower section of the tank. A mixed oil, water and gas fluid is introduced into the upper section of the conical frusta section through a tangentially arranged inlet. The conical frustra shaped wall in connection with the tangentially arranged inlet forces the incoming fluid to form a vortex flow in the upper section of the separator tank. The opening allows oil and gas to accumulate in the upper section of the tank and the water phase to flow downwards into the lower section of the tank.
The Applicant considers that the shape and location of the conical frusta shaped wall within the tank places unnecessary size and configuration restrictions on this separator. The location of the conical frusta shaped wall necessitates that the upper section of the tank be large enough to establish a flow path of a sufficient length to facilitate separation of oil and water, while the lower part have sufficient space to accommodate a fluid reservoir. The lower section utilises valuable space which could be used for separation.
Another prior compact separator is taught in International Patent Publication WO2008/123973A1. This separator comprises a vessel which includes one or more fluid inlets, one or more gas inlets, a vortex generation zone shaped as an inverse truncated cone, a solids collection zone, a separation zone, one or more fluid outlets, and one or more gas outlets. A fluid mixture containing two fluids of different densities is introduced into the vessel through a fluid inlet. Each fluid inlet extends into the vortex generation zone at an angle having a component tangential to an internal wall of the vortex generation zone at a point on the internal wall proximate to the fluid inlet. Gas is also introduced into the fluid in the vortex separation zone through separate gas inlets to facilitate the separation of components of the fluid mixture. The less dense fluid is compelled to agglomerate in the vortex generation zone and rise to the surface of the fluid. Flotation is aided by the gas bubbles which attach, aid and accelerate flotation of the less dense fluid to the surface. The less dense fluid coalesces at the surface and is skimmed from the fluid in the separation zone.
However, the Applicant considers that the introduction of gas bubbles via a separate fluid inlet into the vortex generation zone does not provide optimal separation. Gas bubbles introduced in this manner have a low probability of attaching to the less dense fluid and therefore provides limited separation assistance to this less dense fluid.
It would therefore be desirable to provide an alternate compact separation apparatus.